Ukip has endorsed Zac Goldsmith, the former Conservative MP who is now standing as an independent in the Richmond Park byelection, which will take place on 1 December.

The party’s interim leader, Nigel Farage, said Ukip would not put up a candidate against Goldsmith, who backed leave in the EU referendum, and its supporters should vote for him to stop the pro-EU Liberal Democrats from winning the seat.

Goldsmith, who was the Conservative candidate for mayor of London in May’s election, resigned as an MP earlier this week after the government’s decision to approve expansion at Heathrow, which he opposes. The Conservatives have said they will not put up their own candidate against Goldsmith.

The Lib Dems, who held the west London seat until 2010, have high hopes of winning it back, thanks to their opposition to Heathrow expansion and their support for the EU. A large majority of voters in Richmond Park voted to remain on 23 June.

Ukip, which came fifth in the seat at last year’s general election, said it respected Goldsmith’s decision to fight Heathrow expansion.

“Zac Goldsmith has resigned on a matter of principle and Ukip admire him for having the courage to do so,” a spokesman said. “Ukip have always believed that Gatwick was a preferred option to Heathrow.

“Recognising Zac as a principled man, who was fully committed to helping get Britain out of the European Union, Ukip leader Nigel Farage, in conjunction with our national executive committee, have agreed that we will not be fielding a candidate in the upcoming byelection for Richmond Park.”

The spokesman said the Lib Dems were “committed to overturning the result of the 2016 referendum and ignoring the will of the British people. This must not be allowed to happen.”

“Goldsmith claimed Brexit has nothing to do with this byelection,” he said. “The very public endorsement he has picked up from the party of Nigel Farage nails that lie.

“This byelection presents a golden opportunity to defeat one of the leading Brexiteers, who is determined even [to] take Britain out of the single market. He might be able to afford the huge damage this would do to our economy, but many people in Richmond Park are worried about the effect on their jobs and livelihoods as a result of the Conservative government playing Russian roulette with the British economy.

“Zac Goldsmith can get as many hard-right candidates to give him a clear run as he likes; he knows he faces a major battle with a Liberal Democrat party determined to keep Britain open, tolerant and united.”

On Wednesday, the Labour frontbenchers Clive Lewis and Jonathan Reynolds, as well as the former shadow minister Lisa Nandy, suggested their party should not contest the seat, where Labour came third in 2015. The trio said it would be preferable not to split the progressive vote, with the Lib Dems standing a chance of reducing Theresa May’s Commons majority.

However, Labour’s NEC has decided it will contest the seat. Senior party figures, including the deputy leader, Tom Watson, were angered at the suggestion that the party would not field a candidate in the byelection.

Lib Dems pull off shock victory in Richmond Park by-election as Zac is thrown out

A ‘shockwave to Downing Street’ has, last night, been pulled off by the Liberal Democrats, with Sarah Olney defeating Zac Goldsmith in the Richmond Park by-election.

Lib Dem challenger Ms Olney overturned Mr Goldsmith’s 23,015 majority to win by 1,872 votes. The result saw Ms Olney poll 20,510 votes to Mr Goldsmith’s 18,638, on a turnout of 41,367, or 53.6 per cent. The 21.74 per cent swing to the Lib Dems from Mr Goldsmith topped the 19.3 per cent swing the Lib Dems achieved from the Tories in the Witney by-election.

A Green Party spokesperson said: “The Green Party’s decision to stand down and the huge drop in the Labour Party vote show that people will vote tactically. It proves that there is a huge appetite and a need for proportional representation so that people can express a real preference at elections. In Sarah Olney, we now have an MP who will push for the electoral reform that we so urgently need. We look forward to working with the Liberal Democrats, Women’s Equality Party and the Labour Party in a Progressive Alliance for the 2018 local elections and the next General Election.”

Ms Olney said the shock victory was a rejection of the “Ukip vision” of Britain, and the politics of “anger and division”.

In her victory speech, she said: “The people of Richmond Park and North Kingston have sent a shockwave through this Conservative Brexit government, and our message is clear: we do not want a hard Brexit. We do not want to be pulled out of the single market, and we will not let intolerance, division and fear win.”

In a brief acknowledgement of the result, a clearly downcast Mr Goldsmith said: “This by-election that we have just had was not a political calculation, it was a promise that I made and it was a promise that I kept.”

Labour’s Christian Wolmar lost his deposit as he trailed a distant third with 1,515 votes, losing 8% of the Labour vote compared to 2015.

A Conservative Party spokesman said the result would make no difference to Brexit plans, stating: “This result doesn’t change anything. The Government remains committed to leaving the European Union and triggering Article 50 by the end of March next year. Commiserations to Zac Goldsmith on his defeat. We are sorry that he is no longer in the House of Commons.”

Lib Dem leader Tim Farron said: “The message is clear: The Liberal Democrats are back and we are carrying the torch for all of those who want a real opposition to this Conservative Brexit government.

“This was a remarkable, come-from-nowhere upset that will terrify the Conservatives. A year and a half ago, their man won by nearly 40% and had a majority of more than 20,000. In one fell swoop we have wiped that out completely.

“If this was a general election, this swing would mean the Conservatives would lose dozens of seats to the Liberal Democrats – and their majority with it.

Mr Wolmar said voters had disliked Mr Goldsmith’s “ghastly, disgusting” bid to be London Mayor in which Labour accused him of running a racist campaign against Sadiq Khan.